add two compaction triggers

Signed-off-by: Alex Chi <iskyzh@gmail.com>

pageserver/src/tenant/timeline.rs

@@ -3749,7 +3749,9 @@ impl Timeline {
 
         if new_layers.is_empty() && deltas_to_compact.is_empty() {
             // If L0 does not need to be compacted, look into other layers
-            return self.compact_tiered(layer_removal_cs, target_file_size, ctx).await;
+            return self
+                .compact_tiered(layer_removal_cs, target_file_size, ctx)
+                .await;
         }
 
         // Before deleting any layers, we need to wait for their upload ops to finish.
@@ -3818,6 +3820,40 @@ impl Timeline {
         Ok(())
     }
 
+    fn get_compact_task(tier_sizes: Vec<(usize, u64)>) -> Option<Vec<usize>> {
+        let size_ratio = 1.0;
+        let space_amplification_ratio = 2.0;
+
+        // Trigger 1: by space amplification, do full compaction
+        let total_tier_size = tier_sizes.iter().map(|(_, size)| *size).sum::<u64>();
+        let (_, last_tier_size) = *tier_sizes.last().unwrap();
+        let estimated_space_amp = last_tier_size as f64 / (total_tier_size - last_tier_size) as f64;
+        if estimated_space_amp > space_amplification_ratio {
+            info!("full compaction triggered by space amplification");
+            return Some(
+                tier_sizes
+                    .iter()
+                    .map(|(tier_id, _)| *tier_id)
+                    .collect::<Vec<_>>(),
+            );
+        }
+
+        // Trigger 2: by size ratio
+        let mut total_size_up_to_lvl = 0;
+        let mut compact_tiers = Vec::new();
+        for (tier_id, size) in tier_sizes {
+            if total_size_up_to_lvl != 0 {
+                if total_size_up_to_lvl as f64 / size as f64 > size_ratio {
+                    info!("full compaction triggered by size ratio");
+                    return Some(compact_tiers);
+                }
+            }
+            total_size_up_to_lvl += size;
+            compact_tiers.push(tier_id);
+        }
+        None
+    }
+
     async fn compact_tiered_phase1(
         &self,
         _layer_removal_cs: DeleteGuard,
@@ -3826,9 +3862,10 @@ impl Timeline {
     ) -> Result<Option<CompactTieredPhase1Result>, CompactionError> {
         let guard = self.layers.read().await;
         let (layers, _) = &*guard;
-        
-        // Only compact if enough layers have accumulated.
+
+        // Precondition: only compact if enough layers have accumulated.
         let threshold = 8;
+        assert!(threshold >= 2);
         if layers.sorted_runs.len() < threshold {
             debug!(
                 level0_deltas = layers.sorted_runs.len(),
@@ -3838,8 +3875,57 @@ impl Timeline {
         }
 
         // Gather the files to compact in this iteration.
+
+        let tier_sizes: Vec<(usize, u64)> = layers
+            .sorted_runs
+            .iter()
+            .map(|(tier_id, layers)| (*tier_id, layers.iter().map(|layer| layer.file_size()).sum()))
+            .collect::<Vec<_>>();
+
+        let Some(tier_to_compect) = Self::get_compact_task(tier_sizes) else {
+            return Ok(None);
+        };
+
+        if tier_to_compect.len() < 2 {
+            return Ok(None);
+        }
+
+        let mut deltas_to_compact_layers = vec![];
+        for (tier_id, layers) in layers.sorted_runs.iter() {
+            if tier_to_compect.contains(tier_id) {
+                deltas_to_compact_layers.extend(layers.iter().cloned());
+            }
+        }
+        drop_rlock(guard);
+
+        let deltas_to_compact_layers = deltas_to_compact_layers
+            .into_iter()
+            .map(|l| self.lcache.get_from_desc(&l))
+            .collect_vec();
+
+        let lsn_range = {
+            let lsn_range_start = deltas_to_compact_layers
+                .iter()
+                .map(|l| l.get_lsn_range().start)
+                .min()
+                .unwrap();
+            let lsn_range_end = deltas_to_compact_layers
+                .iter()
+                .map(|l| l.get_lsn_range().end)
+                .max()
+                .unwrap();
+            lsn_range_start..lsn_range_end
+        };
+
+        info!(
+            "Starting tier compaction in LSN range {}-{} for tiers {:?}",
+            lsn_range.start, lsn_range.end, tier_to_compect
+        );
+
+        layers.dump(false, ctx);
+
         // TODO: leverage the properties that some layers do not overlap, kmerge is too costly
-       
+
         // This iterator walks through all key-value pairs from all the layers
         // we're compacting, in key, LSN order.
         let all_values_iter = itertools::process_results(
@@ -3991,7 +4077,11 @@ impl Timeline {
 
         drop(all_keys_iter); // So that deltas_to_compact is no longer borrowed
 
-        Ok(None)
+        Ok(Some(CompactTieredPhase1Result {
+            new_layers,
+            new_tier_at: *tier_to_compect.last().unwrap(),
+            removed_tiers: tier_to_compect,
+        }))
     }
 
     ///